Battery protection systems typically sense battery condition when the battery is not being charged, as for example, when the engine of the vehicle is off. Should a load remain on after the vehicle is turned off, the load will be disconnected before the battery is completely discharged. However, when a partially discharged battery is disconnected from its load, the voltage appearing across the battery increases. Thus, measured voltage increases to an open circuit voltage, which could cause the load to be reapplied, resulting in a cyclic disconnect and reconnect operation. Further, during normal vehicle starting operations, sensed battery voltage will drop substantially due to the large current drain of the starting solenoid, but the system must not disconnect the loads.
In some prior systems, such as U.S. Pat. No. 4,902,986, the system must be manually reset by the operator in order to start the vehicle engine after the loads have been disconnected. Some of these systems such as U.S. Pat. No. 4,493,001 also require special connections to other elements of the vehicle in order to reconnect the load. All of these special requirements and equipment are costly and inconvenient to the vehicle operator, who preferably should be able to start the vehicle by doing nothing more than inserting and turning the ignition.